A thermodynamic model has been developed for the system As-Fe by combining the Calphad approach and the first-principles total energy calculations. Our first-principles calculations are based on the projector augmented wave method within the generalized gradient approximation. We performed these calculations because the experimental values for the enthalpy of formation of the compounds As2Fe, AsFe and AsFe2 may have a large uncertainty. Our results indicate significantly more negative values for the enthalpy of formation of these compounds relative to the experimentally established values. We demonstrate that applying our first-principles results in a thermodynamic analysis based on the Calphad approach leads to a calculated phase diagram and thermodynamic properties which are not significantly different from experimental data. (C) 2008 Elsevier B.V. All rights reserved.